What Is Fast Glass?
June 27, 2011
Not to be too technical here, fast glass also known as fast lens are lenses that have a larger maximum aperture or lower f-stops, like F/2.8, F/1.8 and F/1.4. It does not refer to the auto focus system of the lens, so even if the lens is equipped with the latest autofocus mechanism such the USM or HSM (sigma) and can acquire focus really fast, it’s not necessarily a fast lens. So if you happen to notice a F/2.8 on the specification or description of the lens then it is a fast lens. A lens with a minimum aperture of F/2.8 and wider are considered to fast lenses (F/2.8, F/2.0, F/1.8 F/1.4, F/1.2 with F/1.2 being the fastest and more low light capable and certainly the most expensive.).
But what exactly is it and do we really need it? Since a fast lens has a larger maximum aperture it’s aperture ring has a larger opening compare to non fast lens like the kit lens, therefore allowing more light to reach the sensor faster, and because more light was able to reach the sensor faster it then allows the photographer to use a faster shutter speed. Also, fast lenses will give us a really nice background bokeh, which are perfect for portraiture or close-up and macro.
Do we really need it? The simple answer is yes and no. Fast glass are expensive and not everyone can afford it, so yes if you can afford it, it’s certainly good know that you have one anytime you need it. Fast glass is essential especially when shooting in low light to capture important scene or to freeze the action. On the other hand with the advancement of technology, camera bodies are now getting powerful to the extent that you can get away by increasing your ISO even to a 1000 or even more and will still give you great images. Take for example this photo below which was taken using my EF 70-200mm F/4L IS USM lens, it’s an F/4 lens which is really isn’t enough when shooting sports especially in a stadium that lights aren’t really something to be desired. The photo was shot using the Canon EOS 60d set at ISO 1000.
So should we really go with a fast glass? What I can recommend is, just save up for a fast glass. A fast glass is always a better and will help a talented photographer capture more stunning photographs.